In data processing techniques, prior to its processing in a data processing installation, data must be acquired in suitable form of presentation on data carriers (data media), so that the data can be transmitted from the carriers to the data processing installation and fed into it. It is possible to acquire the data by machine or also visually. In this process, errors can appear due to various causes. Such causes, for example, are faulty data carriers (data media) or faulty data signals, functional defects or construction defects in the equipment (devices) used for data acquisition, errors in operation or also external interference effects such as, for instance, electromagnetic or optical interferences.
Especially in the case of manual data acquisition and data transmission with longer sequences of characters, errors can be caused by a mix-up of characters, omission of characters or feeding in one and the same character more than once. Furthermore, disturbances are possible due to poor legibility of received signals. Such cases frequently occur also when character sequences having been intended for data recognition by machine have been degraded in their legibility so that they must be acquired manually, i.e. visually.
In order to avoid errors of the above-described type within the scope of data acquisition and data transmission to the data processing installation, check characters are used which are acquired and/or transmitted simultaneously with a sequence of characters to permit a check of the sequence of characters for its correctness.
Frequently, modulo-n check characters are used which in the simplest case, for instance in the transmission of numerical sequences, identify the sum of digits or the complement of the sum of digits of the respective numerical sequence due to the fact that in each case, they show the difference between the sum of digits and the next lower or next higher integer multiple of the number n where n corresponds to the number of possible digits per digit position. In the case of the acquisition and transmission not of numerals, but of other character presentations, check characters can be similarly produced by assigning a numerical value to them.
Check characters can, of course, be relatively easily produced or generated with a data processing installation or also with electronic coding installations. In many cases, however, especially in the data acquisition, direct access to such installations is not possible. There are many applications in which access to sophisticated electronics equipment does not exist, for instance, in the use of simple devices to mark goods with prices and/or article identification numbers, in the case of stationary printing machines for the generation of data carriers whose characters are to be legible, in the case of decade switches (contactors) which are capable of being set to a certain definite sequence of numerals or also in the case of meters for electric current, gas or water consumption. Especially in the case of printing machines, in which character wheels are set by machine to the desired sequence of characters in each particular case, the functional reliability can be increased by a check character which is produced simultaneously with the respective data character sequence and printed jointly with it.
If, in these and similar cases, a check character is automatically produced simultaneously with the data acquisition, the data reliability can be increased and thereby the possibility of errors, also in the subsequent data transmission, can be considerably decreased and perhaps even eliminated.